1. Field of the Invention
The present invention relates to head control units for controlling a head such that the head seeks information at the center of the target track on a disk, such as a floppy disk (FD), during a reproduction operation.
2. Description of the Related Art
In a conventional floppy-disk drive apparatus, a step driving mechanism employing a stepper motor is used as a head feed unit for moving a head to a track where recording is to be performed concentrically on a recording plane of a disk. With a mechanical step operation of this head feed unit, the head is positioned at the track. Instead of the step driving mechanism, a head feed unit having a linear-motor drive is provided for some floppy-disk drive apparatuses to move the head continuously.
In a disk apparatus of such a type, a detection section detects a return of the head to the origin and reports it to the host computer. To move the head to the target track of a disk, the host computer sends seek instruction pulses formed of STEP pulses one for one track and a seek request direction to the disk apparatus. According to this seek instruction pulses, the disk apparatus moves the head by the number of tracks corresponding to the seek instruction pulses.
In apparatuses such as the conventional floppy-disk drive apparatus, a screw shaft driven by a stepper motor is engaged with a head base and the head is fed by the rotation of the screw shaft. Since the mechanical connection determines the relationship between the rotation of the stepper motor and the movement position of the head, the head is moved to the target track just by driving the stepper motor according to the seek instruction pulses sent from the host computer.
On the other hand, in apparatuses employing a head feed unit having a linear-motor drive, since a head base has flexibility in the head feed unit, a detection section for always detecting the movement position of the head needs to be provided.
Such a head feed unit having a linear-motor drive is, for example, included in a disk apparatus in which a high-density-recording disk on which a servo signal is recorded for tracking and a floppy disk (FD) having a capacity of 2 megabytes (MB) can be loaded. The high-density disk to be loaded into this type of a disk apparatus is also a flexible disk. In the following description, a flexible disk having a capacity of 2 MB is called a floppy disk and it is discriminated from the high-density disk.
When the high-density disk is loaded, the head is moved by a linear-motor drive. When the head reads the servo signal, it is determined that the head has been positioned at a track. On the other hand, when a floppy disk is loaded, the head feed position is controlled according to the detection output of the detection section and the head is positioned at the track.
FIG. 14A shows an example detection output of the detection section provided for the disk apparatus. This type of detection section is formed, for example, of a scale having fixed-interval slits provided for one of the moving side and the fixed side and a pair of optical detection devices provided for the other side. As the head base moves, phase-A and phase-B detection outputs having a relative phase difference of one-fourth the period (90 degrees) are obtained from the pair of the optical detection devices.
In FIG. 14A, the horizontal axis indicates the head movement position in the radial direction of the disk and the phase of the phase-B detection output, and the vertical axis indicates the strength (voltage) of the detection outputs. As shown in FIG. 14A, the phase-A detection output and the phase-B detection output have the relationship of the sine curve and the cosine curve, or curves approximating to these trigonometric functions.
As shown in FIG. 14A, detection data to be used is switched from the phase-A detection output to the phase-B detection output and vice versa at intersections of both detection outputs. As a result, the movement position of the head is detected with the use of a part of the detection outputs, which shows linearity and is indicated by a solid line in FIG. 14A. FIG. 14B shows head positions calculated according to the detection data, shown by the solid line in FIG. 14A. The horizontal axis indicates the phase of the phase-B detection output and the vertical axis indicates the detected value of the head position.
As shown in FIG. 14A, with the alternate use of the parts of the detection outputs, which show strong linearity, the relationship between the detection outputs and the head position is obtained with a high precision as a relationship approximating to a linear function, as shown in FIG. 14B. When the position of the detection section is adjusted such that the positions corresponding to phases of 0 degrees, 360 degrees, 720 degrees, . . . of the phase-B detection output match the centers of tracks, the positional deviation from the head position to a track center is always obtained positively.
When the output value of the detection section is abruptly shifted due to the movement of the head caused, for example, by an external impact, since the detection output linearly relates to the head position as shown in FIG. 14B, it is easily determined whether the head has been moved toward the center of the disk or toward the outside.
In the detection section, described above, which uses the scale having the slits and the pair of optical detection devices, the machining tolerance of the slits in the scale or an error in the relative positions of the pair of the optical detection devices cannot be eliminated. An error in the phase difference between the phase-A detection output and the phase-B detection output cannot be avoided as shown in FIG. 14A. In an actual apparatus, it is possible that the phase difference between the phase-A and phase-B detection outputs is shifted by about xc2x130 degrees from a reference of 90 degrees.
FIG. 15A shows a case in which the phase-A detection output is shifted from the phase-B detection output by 30 degrees measured from an original phase difference of 90 degrees.
The position of the detection section is adjusted such that the head is positioned at the centers of tracks on the disk when the phase-B detection output is 0 degrees, 360 degrees, 720 degrees . . . . Under this condition, when detection data to be used is switched from the phase-A detection output to the phase-B detection output and vice versa at the same timing as that in FIG. 14A, the detection data to be used has steps at the switching points of both phase detection outputs, as shown in FIG. 15A. FIG. 15B shows the relationship between the phase (horizontal axis) of the phase-B detection output and the detection value (calculated value) of the head position. Since a phase tolerance is formed between the phase-A and phase-B detection outputs as shown in FIG. 15B, the detected position includes incontinuous points.
While the head is gradually approaching the center of the target track and the head-movement speed is decreasing, for example, when the head reaches an incontinuous point shown in FIG. 15B, speed control servo responds sensitively in head seek control and the head is likely to become uncontrollable or a seek error is likely to happen such as a to-and-fro repeated movement of the head.
On the other hand, it is possible that a one-phase detection output is obtained from the detection section and the head position is detected according to the one-phase detection output. In this case, around the peaks of the one-phase detection output, detection-output linearity cannot be obtained. While the detection output is around its peak, if the head is moved by an external impact and the detection output exceeds its peak point, it becomes impossible to determine the direction in which the head has been moved. As a result, a track counting error occurs.
The present invention has been made to solve the above conventional drawbacks. Accordingly, it is an object of the present invention to provide a head control unit used for a disk apparatus, which is unlikely to generate a track counting error.
Another object of the present invention is to provide a head control unit used for a disk apparatus, which allows a head-position detection and a positional deviation from the center of the target track to be obtained accurately and which is unlikely to generate a seek error, even if the phase difference between two-phase detection outputs used has a tolerance.
One of the foregoing objects of the present invention is achieved through the provision of a head control unit in a disk apparatus having a rotation driving section for driving a disk, a head facing a recording surface of the disk, head feeding means for feeding the head in a direction in which the head traverses tracks on the disk, a detection section for generating a detection output changed according to the movement of the head, and a control section for controlling the head feeding means according to the detection output obtained by the detection section, wherein the detection section outputs phase-A and phase-B detection outputs having different phases and having polarities changing at an interval of half the period according to the movement of the head; and the control section controls such that it is determined from a combination of the polarity of the phase-A detection output and that of the phase-B detection output that the head has been moved to an adjacent track, the track number of the current head position is incremented or decremented by 1, an intra-track deviation from the current head position to the center of the track is detected by the use of either the phase-A detection output or the phase-B detection output, a deviation from the current head position to the center of the target track is calculated from the track number and the detected intra-track deviation, and the head feeding means moves the head according to the deviation from the current head position to the center of the target track.
The present invention is suited to a system which uses head feeding means having flexibility in moving the head as in a case in which the head is driven by a linear motor.
In the present invention, the detection outputs having two different phases are obtained by the detection section. From one of the two detection outputs, the positional deviation from the current head position to the center of the track is obtained in an analog manner, and the head position in the track is obtained from the combination of the polarity of the phase-A detection output and that of the phase-B detection output in a digital manner. Therefore, even if the head is moved due to an external impact and a detection output exceeds its usual peak, the zone where the head is positioned in the track can be determined from the polarity of the phase-A detection output and that of the phase-B detection output. As a result, if the head is moved by impact, the head position is recognized and a track counting error does not occur.
It is preferred that the head control unit be configured such that the phase-A detection output and the phase-B detection output basically have a phase difference of one-fourth the period, one track is divided into four zones each having a different combination of the polarity of the phase-A detection output and that of the phase-B detection output, a track-number difference between the number of the target track and that of the track where the head is positioned and an intra-track deviation from the current head position to the center of the track are detected in each of the four zones, and a deviation to the center of the target track is calculated from the track-number difference and the intra-track deviation.
With one track being divided into the four zones, the positional deviation from the current head position and the center of the target track can be relatively easily calculated.
It is preferred that the head control unit be configured such that it is anticipated that the phase-A and phase-B detection outputs have a relative phase-shift tolerance, and whichever of the phase-A and phase-B detection outputs used for detecting the intra-track deviation is provided with a dead zone where the relative phase-shift tolerance may be generated and detected values are fixed.
In the present invention, the head position and the positional deviation can be obtained without the dead zone. When the phase-A detection output and the phase-B detection output have a relative phase-shift tolerance, however, the positional deviation has an incontinuous part corresponding to the tolerance. In this case, this incontinuity may adversely affect a seek operation. Therefore, with the dead zone being provided, if the relative phase-shift tolerance is generated, a precise head seek operation is implemented irrespective of the phase shift.
It is preferred that the head control unit be configured such that the control section performs speed control for sending a speed control signal to the head feeding means when the head approaches the target track; a detected speed difference is obtained from a difference between the current detected movement speed of the head and a target speed specified according to the deviation from the current head position to the center of the target track, and a compensation gain is set in the speed control signal according to the detected speed difference; and the compensation gain is increased when the head passes through the dead zone provided for the target track and approaches the center of the target track.
When the dead zone is provided, the head position is detected in the dead zone as if the head were stopped. Therefore, when the head passes through the dead zone and approaches the center of the target track, control is performed such that the head speed is abruptly increased. Since the head can be decelerated with the use of the gain control when the head has passed the dead zone, the head is promptly stopped at the target track.
It is preferred that the head control unit be configured such that, in the control section, when the head is positioned at the center of the target track, on-track control for sending an on-track control signal to the head feeding means is performed, and a proportional gain for compensating for the deviation from the current head position to the center of the target track is set in the on-track control signal in the on-track control; and when the head approaches the center of the target track, the speed control is switched to the on-track control at a first switching point where the head is positioned a predetermined distance away from the dead zone in the target track, the on-track control is switched to the speed control at a second switching point where the head is moved away from the center of the target track after the control has been switched to the on-track control, and the second switching point is disposed at a position farther away from the center of the target track than the first switching point.
It is further preferred that the second switching point match an end of the dead zone, closer to the center of the target track.
When the second switching point, where the on-track control is switched to the speed control when the head is moved away from the center of the target track under the on-track control state, is disposed at a position farther away from the center of the target track than the first switching point, where the speed control is switched to the on-track control when the head approaches the center of the target track to be on the track, the head is quickly moved to a point near the center of the target track when the head is moved to the center of the target track, and on-track recovery is stably performed when the head leaves the center of the target track. Therefore, an on-track state is easily maintained even if vibration or impact is applied.
As described above, since a seek operation toward the center of the target track is performed with the use of both phase-A detection output and phase-B detection output obtained by the detection section in the present invention, a track counting error is prevented in updating.
Since the dead zone is provided for a detection output used for obtaining a positional deviation, even if the phase difference between the phase-A and phase-B detection outputs has an error, the positional deviation from the head to the center of the target track is accurately obtained and a seek error is prevented.
In addition, since the gain is set in the speed control, an uncontrollable movement of the head is prevented when the head has passed the dead zone. Because the switching points between the speed control and the on-track control are specified, the head is quickly moved to the center of the target track and the head is made stable at the on-track state.